130 U. S. BUREAU OF FISHERIES 



With rainbow fingerlings (fig. 2) sheep liver made a somewhat 

 better showing, although it was still decidedly inferior to beef liver. 

 Fish on a straight diet of sheep liver showed a high mortality, 

 but when the liver was combined with other products fairly good 

 results Avere obtained. Although brook-trout fingerlings on the 

 same combinations showed a better growth and lower mortality 

 than on straight sheep liver the improvement was not as marked 

 as with the rainbows. 



Both brook and rainbow yearlings did well on a diet of straight 

 sheep liver, no unusual mortality appearing. Although the latter 

 species again did somewhat better the results, in general, were not 

 sufficiently encouraging to warrant the use of sheep liver in prefer- 

 ence to other and cheaper meats. 



FRESH FISH 



Hatcheries located near an available supply often make use of 

 fresh fish in considerable quantities. The fish used consist usually 

 of " rough," inferior species, unpopular with the trade, and selling 

 at prices attractive to the hatchery operator. As there has always 

 been more or less prejudice and difference of opinion as to the 

 suitability of fish as a trout food, the 1928 feeding program at 

 the Pittsford hatchery included some lots of fingerling and yearling 

 brook trout on fresh fish diets. A few lots of rainbow fingerlings 

 were also used. 



The fish was donated by the General Seafoods Corporation, 

 Gloucester, Mass., a carton of freshly frozen packages being shipped 

 each week. This consisted of " bone loaf," herring, and mackerel. 

 " Bone loaf " is a by-product of the fillet industry, being made from 

 the bones and whatever flesh adheres to them after the filleting 

 process. It was received in a frozen condition, finely ground, and 

 compressed into bricklike cakes. The herring used consisted of 

 the whole animal, and the mackerel of heads and fin scrap, both 

 kinds of fish being ground fine and frozen. 



Tlie brook-trout fingerlings on the herring ration made the best 

 growth (fig. 9), those on "bone loaf" next, while the fish on mack- 

 erel made a very poor showing. The addition of 50 per cent beef 

 liver to the " bone-loaf " ration gave greatly improved results and 

 indicated a possible way to make use of this product if it were 

 ever put on the market as a food for trout. Results with the fish in 

 general were, however, greatly inferior to those obtained from the 

 standard meats. 



A real o))jection to these fish products was the fact that they 

 thawed quickly and were then very difficult to keep fresh — mackerel 

 being particularly unpleasant. This was very greasy and spoiled 

 easily. 



The mortality following the use of the straight fish rations was 

 consistently very higli in the brook-trout lots. The rainbow finger- 

 lings, on the other hand, did fairly well, making a good growth, 

 accompanied by a moderate nioi'tality. Tliis fact again indicated 

 the greater tolerance and adaptability of the rainbow for hatchery 

 conditions in general. 



Brook-trout yearlings were fed no "bone loaf" but received tlic 

 mackerel and the herring with results inferior to those obtained 



